1. Field of the Invention
The present invention relates generally to a system and method for broadcasting, receiving and using television schedule information. More particularly, it relates to such a system and method in which the television schedule information is broadcast in, e.g., the vertical blanking interval (VBI) of a television broadcast, a schedule of television programs for a user's broadcast area or cable system is compiled from the broadcast, and the schedule is displayed on the user's television set for interactive use. As used herein, the term "broadcast" is used in a broad sense to include such transmission modes as cable and telephonic transmission.
2. Description of the Prior Art
It is known in the art to provide an interactive television program schedule system utilizing broadcast schedule information. For example, such a schedule system is disclosed in commonly assigned Young, U.S. Pat. No. 4,706,121, issued Nov. 10, 1987 and the above referenced Young et al. pending application.
In the design of such a schedule system, only a limited amount of memory and data processing capability can be provided in the user's equipment that receives the schedule information broadcast, compiles the schedule for the user's broadcast area or cable system, displays the schedule on the user's television set and interacts with the user, while enabling that equipment to be provided at a low enough price for mass marketing. This memory and data processing limitation was recognized by Hallenbeck, U.S. Pat. No. 5,038,211, issued Aug. 6, 1991. The solution proposed by Hallenbeck is to subdivide the schedule information into prioritized categories, store the highest priority category, and as much of the lower priority categories as possible in the amount of memory available. A significant problem with this approach is that less information may be provided about programs in the schedule when there are more programs in the schedule and the need for more information is greatest. Further development in light of the memory and processor limitations of consumer electronics is therefore required.
When schedule information is transmitted as part of a program broadcast signal and a prior art subscriber unit acquires the schedule information from the program broadcast signal, a potential problem arises when previously broadcast programs have been recorded on a VCR and are played back. The prior an subscriber unit lacks any ability to distinguish a video signal generated from a recorded program from a video signal received in real time from a broadcast. As a result, the subscriber unit may overwrite more recent program schedule information acquired from a real time broadcast with older program schedule information coming from a video tape.
Proposals to transmit television schedule information with television broadcast signals often use a low bandwidth transmission mode, such as one or more lines in the vertical blanking interval (VBI) of the television broadcast signals. The use of such low bandwidth transmission modes means that the format and management of the transmissions must be carefully planned in order to avoid practical problems. For example, when a schedule update is to be transmitted, unless special provisions are made for such updates, worst case transmission delay until the update is received and entered in a user's subscriber unit could amount to five hours, the time for transmission of a complete schedule for a week in an NTSC television broadcast signal using one line of the VBI for the schedule information. In the case of last minute schedule changes, such a delay would be unacceptable.
Data encryption is essential for a subscription-based broadcast television schedule system. Without data encryption, the schedule information could be acquired and used by pirate user equipment without payment of the subscription fee. However, decryption of encoded data is a processor intensive. A conventional approach of encrypting the entire schedule information transmission requires a faster and more expensive microprocessor than would otherwise be suitable for the subscriber units.
When implementing a television schedule system on a national or even international basis, provision must be made for different time zones. Adjusting times in the schedule for the different time zones in the process of transmitting the schedule adds substantial overhead to the data transmission. It would be desirable to eliminate the need for such adjustments in the transmission.
It may be desirable in the operation of a television schedule system to provide the schedule information embedded at different places in the television signal at different parts of the system in order to avoid the necessity of imposing uniformity throughout the system. To do so, it is necessary to provide a way for recipients of the schedule information to identify it in the television signal.
In the operation of a broadcast television schedule system, acquisition of new schedule information by the subscriber units consumes a substantial proportion of available microprocessor processing time. When obsolete schedule information is deleted and new schedule information is acquired, a substantial portion of the new information, such as program titles, duplicates information already present in stored schedule information or to be deleted with the obsolete schedule information. Avoiding the deletion of information that will form part of new schedule information would help to minimize the amount of processor time devoted to the acquisition of new schedule information.
Because of the severe memory limitations in consumer electronic products, it is necessary to use the memory efficiently in order to provide as much information and as much functionality in the subscriber unit as possible with the available memory.